The invention relates to torque transmitting apparatus in general, and more particularly to improvements in apparatus for transmission of constant torque.
It is often necessary to rotate one or more components at a constant toque. Examples of such components are reels or spools for webs of photographic material in printing and like machines. In a printing machine, a combined takeup and payout reel or spool receives webs of photographic material from advancing bands or rolls, and the leader of a web is automatically attached to the core of the reel. The same set of advancing bands or rolls, or a different set, is used to draw the web off the reel and the trailing end (formerly the leader) of the web is automatically detached from the core of the reel. The reel should be driven with a constant force, i.e., the means for rotating the reel must transmit a constant torque, because any abrupt changes of torque can entail breaking of the web, inaccurate positioning of the web relative to the platform of the printer and other undesirable consequences. It is important to ensure that the reel be driven at a constant torque in both directions, i.e., to collect or to pay out a web of photographic film, photographic paper or the like.